Circuitry to send signals between components of a digital system, such as a computer system, are well-known. One known approach for sending signals between components of such digital systems is to use a single-ended signal. However, the signal speed, or frequency, of single-ended signals is limited to certain magnitudes depending on the technology before the signals are impaired by noise. A solution to the limitations of the single-ended signal is the differential signal which allows for faster signal speeds while reducing the effects of noise at such high speeds. Noise is reduced in the differential signal because the differential signal is based on the difference between two signals, such as a clock and an inverted clock. The combination of the two signals helps to cancel some of the noise. For instance, if the two signals are routed in close proximity, both signals are likely to experience the same noise. In which case, the difference between the two signals is likely to be largely unaffected by the noise.
A drawback of using differential signals is that components of older, slower systems that use single-ended signaling cannot be used in faster systems that use differential signals. Even if selected, faster differential input circuits cannot be driven by single-ended (slower) signals. Furthermore there is no interchangeability between the two approaches, and therefore, in order to facilitate the selection between a single-ended and a differential signal, receivers on printed circuit boards needed to be physically changed.
Another drawback of current differential input signal buffers is that an external reference voltage is required utilizing external resistors and capacitors. Utilizing external resistors and capacitors for the external reference voltage can cause variability of the resistors and the capacitors.